Implant and Implant System

ABSTRACT

An implant system for implantation at a joint, the implant system including an implant device, the implant device comprising a body portion having first and second ends, and a first elongate member, extending from the first or second end of the body portion, the implant system further comprising a corresponding fixation device for securing the first elongate member to a subject, the fixation device comprising at least one latching element, the first elongate member comprising at least one cooperating element, the at least one cooperating element being capable of cooperating with said at least one latching element of the fixation device in use.

This application is a continuation of U.S. application Ser. No.14/123,918, filed Dec. 4, 2013, now U.S. Pat. No. 9,283,077, which is anational stage of PCT Application PCT/GB2012/051284, filed Jun. 7, 2012,which in turn claims priority to Great Britain Patent Application1109515.5 filed Jun. 7, 2011.

FIELD OF THE INVENTION

The present invention relates to implants and implant systems forimplantation in a joint of a human or animal subject.

BACKGROUND TO THE INVENTION

Meniscal injuries account directly for over 50% of all surgery performedon the knee. Tears of the meniscus can occur at any age, but acute tearsare most common in the 20 to 40 age group. These tears are more commonin men and are often associated with sporting activities, such as tennisand football. Estimates at the incidence of acute tears vary between 24to 60 per 100,000 population per year (Clayton & Court-Brown 2008,Arendt 1999). Medial meniscal tears occur almost twice as frequently aslateral meniscal tears (Campbell et al. 2001). Increasing age results indegeneration of the meniscal tissue with subsequent tearing. Estimatessuggest that 60% of people aged over 65 have a degenerate meniscal tear.Approximately 850,000 meniscal procedures are performed each year in theUnited States alone (Arendt 1999).

Surgery for meniscal tears, whether acute or degenerate, most commonlyinvolves a partial meniscectomy with resection of the torn region of themeniscus. However, this loss of meniscal tissue is now fully appreciatedto increase the probability of developing degenerative changes in thejoint and accelerate the degeneration in joints with pre-existingosteoarthritis (Hede et al. 1992, Andriacchi et al. 2004, Hunter et al.2006, Roos 2005, Roos et al. 1995), therefore resulting in poor outcome(McDermott & Amis 2006). Consequently the desire is to repair or replacethe meniscus to retain its function. Meniscal repair is an establishedprocedure, but is only effective for a limited number of tears foundsolely in the periphery of the meniscus (Heckmann et al. 2006). Attemptsto regenerate meniscal tissue using scaffolds have thus far failed tocompletely restore meniscal volume and are reliant on the presence of anintact peripheral rim of meniscus (Schonenfeld et al. 2007). Meniscaltransplantation from cadaveric donors is an established technique(Verdonk et al. 2005) which is limited by a lack of supply, risk ofinfection and difficulty sizing the donor meniscus to the recipient.Clinical results at over 10 years show encouraging improvement insymptoms, and delay in progression of osteoarthritic radiographic signsbut meniscal extrusion is seen in almost all cases (Van der Wal et al.2009, Verdonk et al. 2006). While the procedure requires patients to bematched to donors, issues of sizing and compatibility will contribute tothe variation in results seen (Ha et al. 2010, Lee et al. 2010).

Scaffold developers Regen Biologics and Orteq have estimated thepotential value of the global meniscus market at $1.6 and $2 billionrespectively based on replacing 50% of the 1.4-1.5 million partialmeniscectomies estimated to be performed worldwide each year (ReGenBiologics 2009, Tan 2008).

Functional Role of the Meniscus

The menisci are two crescentic, wedge-shaped fibrocartilages lying onthe tibial plateau in the medial and lateral compartments of the knee.They are attached to the underlying bone (tibia) via insertionalligaments at their anterior and posterior horns. Their primary roles areto distribute loading across the joint and to provide passive stabilityacross the range of joint motion (Bullough et al. 1970, Seedhom 1976,Kurosawa et al. 1980, Markolf 1981, Levy 1989). Meniscal material iscomposed of about 75% water, about 20% type I collagen fibres and about5% non-collagenous substances (McDevitt & Webber 1990, Wirth 1996).Therefore the tissue is naturally inhomogeneous and composite. Meniscalmicrostructure comprises predominantly of a dense framework ofcircumferentially orientated collagen fibre-bundles, with additionalrandomly orientated fibres tying the circumferential bundles together(Petersen & Tillman 1998). This complex arrangement means that themeniscus is locally anisotropic, providing stiffness in thecircumferential direction.

Shape, structure and attachments of the menisci combine to support theprimary load bearing functional role of the tissue (Masouros et al.2008). When the femur bears down onto the tibia (so when the knee jointbears load), the knee joint is subjected to compression. The compressiveforce is distributed across the joint over an articulating contact area,resulting in contact stresses (contact pressure). These stresses areproportional to the load and inversely proportional to the contact area;in other words, the larger the contact area over which the load isdistributed the less the contact stress. However, the geometry of thebony surfaces that articulate at the knee joint are not conformingfully, and therefore do not minimise contact stresses on the underlyingarticular cartilage. The menisci optimise the way the load istransferred through the joint by increasing the conformity of thearticulation; as the femur bears down onto the tibia, the wedgedcross-section of the menisci causes them to extrude radially out of thejoint; this causes their circumference to increase. The meniscalstructure resists this radial displacement by developing tension alongits strong circumferentially orientated fibre-bundles (hoop stresses);this tension is then transferred through the insertional ligaments atthe meniscal horns into the tibia. This load bearing mechanism occursthroughout the whole range of knee motion, as the menisci are mobilestructures, able to conform to the articulating surfaces at anyknee-joint position; this is precisely because the menisci are mainlyattached to the tibia via insertional ligaments at their horns.

Existing Meniscal Replacements

Prior art has attempted to replace the meniscal tissue through either ascaffold system or a synthetic replacement. Scaffolds are intended toreplace tissue removed during a partial menisectomy. They involve theuse of a porous material which is usually sutured to the remainingmeniscal tissue in the hope that tissue ingrowth will occur through thescaffold. Results have shown, however, that due to poor vascularisationin the main body of the meniscus these scaffolds are not successful inpromoting regrowth; due to shrinkage, they often fail to replace theentire lost volume of tissue. Therefore, their long-term ability toreconstruct a functional meniscus remains elusive. Syntheticreplacements have been attempted involving various hydrogel materials,in order to improve the general material properties of the prosthetic.However, few of these synthetic prosthetics provide evidence ofeffective load bearing or mechanical simulation of the meniscus.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided animplant system for implantation at a joint, the implant system includingan implant device, the implant device comprising

-   -   a body portion having first and second ends, and    -   a first elongate member, extending from the first or second end        of the body portion,    -   the implant system further comprising a corresponding fixation        device for securing the first elongate member to a subject, the        fixation device comprising at least one latching element, the        first elongate member comprising at least one cooperating        element, the at least one cooperating element being capable of        cooperating with said at least one latching element of the        fixation device in use.

The invention provides a fastening mechanism for fastening said elongatemember of the implant device to the subject in use. The first elongatemember is a tension member for securing to the subject in use. Thecooperating element of the elongate member cooperates with the latchingelement of the fixation device in use, the latching element andcooperating element suitably providing complementary engagement meansthat engage with one another in use. The fixation device is adapted forfixation relative to a subject, such that the elongate member cansuitably be secured to the subject. The at least one cooperating elementmay comprise any suitable element such as a ratchet tooth, a ridge of athreaded formation such as a buttress thread or other serratedformation, or an aperture in the elongate member for cooperation withthe corresponding latching element. Suitably, the implant device is usedas a replacement for natural tissues, including for example, replacementof a meniscus of the knee joint. Suitably, the implant system is adaptedto provide direct or indirect fixation of the implant device tobiological tissue.

Preferably the implant device comprises a second elongate memberextending from the other of the first or second end of the body portionfrom which the first elongate member extends.

Preferably the implant system further comprises a second correspondingfixation device for securing the second elongate member to a subject,said fixation device comprising at least one latching element, thesecond elongate member comprising at least one cooperating element, theat least one cooperating element of the second elongate member beingcapable of cooperating with said at least one latching element of saidfixation device in use. Suitably, the second elongate member is a secondtension member for securing to the subject in use.

Preferably the first and/or second elongate member is provided with aplurality of cooperating elements, said at least one latching element ofthe corresponding fixation device being capable of cooperating with anyone of the cooperating elements in use. By having a plurality ofcooperating elements, the first or second elongate member can be drawnto a desired tension and said at least one latching element of thefixation device can be engaged with the cooperating element thatprovides the desired tension in said elongate member, such that theelongate member can be secured to the subject under a desired tension.

Preferably the cooperating elements of said plurality of cooperatingelements are spaced apart from one another along at least a portion ofthe length of the elongate member. By providing a plurality ofcooperating elements spaced along the elongate member at discretepositions, the tension exerted on the implant device when secured to thesubject can be varied by varying the cooperating element with which theat least one corresponding latching element engages in use.

The first and/or second fixation device may comprise a plurality oflatching elements, each being capable of cooperating with said at leastone cooperating element of the corresponding elongate member. Thelatching elements of said plurality of latching elements may be spacedapart from one another along at least a portion of a length of saidfixation device.

Preferably said at least one latching element and said at least onecooperating element comprise a ratchet mechanism.

Preferably the ratchet mechanism comprises at least one ratchet elementand at least one ratchet stop, the at least one ratchet element beingcapable of cooperating with the at least one ratchet stop in use.Suitably the at least one cooperating element may be a ratchet elementand the at least one latching element may be a ratchet stop.

The cooperating ratchet element and ratchet stop providing aratchet-like fixation means, which the installer can use to adjustfixation, to optimise the load-bearing function of the implant device.The use of a ratchet mechanism for fixation of the implant device helpsto maintain the ability of the implant device to transmitpressure/compressive loads to the subject's body. The fixation meanshelps to prevent the fixation from moving or relaxing afterimplantation, in response to the cyclic loads imposed in use. Thefixation means also allows for optimised tensioning of the implantdevice during implantation and during subsequent revision procedures tore-tension the implant device if desired. Suitably the ratchet typemechanism allows movement of the elongate member relative to thefixation device in one direction but not in the opposing direction, suchthat the implant device is easy to fit and adjust, but can be securelyfixed to the subject once implanted.

Preferably the first and/or second elongate member has a plurality ofratchet teeth. For example, the first or second elongate member maycomprise a barbed plate or similar. Alternatively, the first and/orsecond elongate member may have a plurality of apertures provided asratchet elements, to cooperate with the at least one ratchet stop on thecorresponding fixation device.

Preferably the first and/or second elongate member terminates in a freeend.

Preferably each ratchet tooth comprises a first surface angled relativeto said elongate member, the first surface sloping towards said elongatemember in a direction towards the free end of said elongate member, anda second surface, which slopes towards said elongate member in adirection away from the free end of said elongate member, said secondsurface being more steeply sloped than said first surface.

Preferably at least a portion of the first and/or second elongate memberis strap shaped. For example, the elongate member(s) may be flat, planarmembers that are tape-like, ribbon-like or belt-like or similar.

Preferably at least a portion of the first and/or second elongate memberis substantially crescent shaped in cross-section. In this case, theconcave side of the crescent cross-sectioned portion of the elongatemember can be curved to substantially correspond to curvature of thefixation device, and the convex side of the elongate member can beshaped to fit against the curved side wall of a tunnel in the subject'sbone for receiving the elongate member. Said elongate element may have aplurality of cooperating elements on the concave side for cooperatingwith the at least one latching element of the fixation device. Saidelongate member may also have fixation means on the convex side forengaging with the bone. The fixation means may be, for example aplurality of ridges such as teeth.

Preferably the first and/or second fixation device is adapted to besecured to a subject's bone in use.

Preferably the first and/or second fixation device is securable to asubject's bone, said fixation device having a lower face that facestowards the bone when secured to the subject's bone, the device havingat least one latching element on its lower face for cooperating withsaid corresponding cooperating element in use.

Preferably said fixation device is shaped to provide a channel betweenthe lower face and the bone when said fixation device is secured to asubject's bone, the elongate member being insertable within the channelin use.

Suitably, the ratchet mechanism allows the elongate member to be movedthrough the channel in one direction (i.e. to tighten the implantdevice) but not the other direction. For example, the elongate membermay have a serrated surface or a plurality of apertures, the fixationdevice being a staple bridging over the elongate member in use andincluding a serrated and/or spiked surface on the underside of thecrossbar of the staple, to engage the serrations and/or plurality ofapertures in the elongate member, providing a ratchet type mechanismallowing movement of the elongate member relative to the fixation devicein one direction but not in the opposing direction. Suitably the ratchettype mechanism can be used to tense and re-tense the implant device. Thestaple-like fixation device may have holes for receiving screws oneither side of the crossbar, to secure the fixation device to thesubject's bone.

Preferably the system includes means for fixing the fixation device tothe bone. Preferably said fixation device is adapted to be screwed orstapled to bone.

Preferably the first and/or second fixation device is externallythreaded, the threading forming a plurality of latching elements capableof cooperating with said at least one cooperating element of thecorresponding elongate member. Suitably, the threading forms a pluralityof ratchet stops capable of cooperating with said at least one ratchetelement of the corresponding elongate member.

Preferably the fixation device is a screw, the screw being externallyhelically threaded.

Preferably the first and/or second elongate member is insertable in atunnel in a subject's bone, the tunnel having first and second openends, the corresponding fixation device being insertable in the secondend of the tunnel, such that the at least one latching element of saidfixation device engages with the at least one cooperating element onsaid elongate member, the corresponding fixation device being securablenon-movably relative to the tunnel, preventing the elongate member frombeing withdrawn from the tunnel via the first open end.

Preferably the implant system further comprises an elongate sheath, thefirst or second elongate member being insertable in the sheath. Thesheath may be receivable in a tunnel formed in the subject's bone

Preferably the sheath has means for non-movably securing it to asubject's bone. Preferably the sheath has means for non-movably securingit within a tunnel formed in a subject's bone. Preferably the sheath hasa first end and a second end, either or both of the first and secondends having two or more longitudinal cuts therein, forming arms in saidend of the sheath, wherein said arms are biased apart from one anotherin use. Suitably the arms flare/splay apart, and push against bone inuse, lodging the sheath in the bone.

Preferably the corresponding fixation device is insertable in thesheath. Suitably, the sheath has first and second ends, the elongatemember being insertable via the first end and the fixation device beinginsertable via the second end.

Preferably the internal surface of the sheath has at least oneprotuberance capable of cooperating with said at least one latchingelement on the corresponding fixation device.

Preferably at least a portion of the sheath is internally screwthreaded, said fixation device being correspondingly externallythreaded, such that said fixation device is capable of securely engagingin the sheath.

By non-movably securing the sheath to the bone and inserting theelongate member in the sheath, the elongate member can be securedrelative to the bone, by securing it to the elongate member. This allowsfor easy exchange of the implant device, for example if the implantdevice material has worn away, without the need forre-drilling/re-cutting in the subject's bone.

Preferably the first elongate member is insertable in a first tunnel ina subject's bone and the second elongate member is insertable in asecond tunnel in a subject's bone, the second elongate member beingprovided with at least one cooperating element, the fixation devicebeing adapted to secure both the first and second elongate members tothe subject, the fixation device comprising at least a first latchingelement for cooperating with the at least one cooperating element of thefirst elongate member and the fixation device further having at least asecond latching element for cooperating with the at least onecooperating element of the second elongate member in use. Suitably, whenbeing implanted at the knee, both elongate members pass throughcorresponding bone tunnels to similar places on the surface of thetibia, wherein the two ends of the elongate members may be folded overone another and secured by the single fixation device onto the surfaceof the tibia. The fixation device may include ratchets stops facing infirst and second directions, for cooperating with ratchet elements onthe first and second elongate members respectively.

Preferably the implant device further comprises a reinforcing element,which extends through the first elongate member and through the bodyportion of the implant device. Suitably the reinforcing element extendscontinuously (i.e. its length is unbroken) through the first elongatemember and through the body portion of the implant device. Thereinforcing element acts as a tension member extending through theimplant device.

Preferably the reinforcing element extends through the first elongatemember, through the body portion of the implant device, and through thesecond elongate member. Suitably the reinforcing member is embeddedwithin the body portion, or may be at its outer surface, and within theelongate member(s). Suitably, the elongate member may have a highermodulus of elasticity than that of the body portion. In this way, theelongate member is sufficiently stiff in order to be pushed/insertedinto a fixation tunnel or channel.

Preferably the elongate element is strap shaped.

Preferably said at least one cooperating element of the first and/orsecond elongate member comprises at least one aperture for receivingsaid latching element of the corresponding fixation device in use, fordirectly securing said elongate member to bone. For example, the fixingmeans may be a screw. Alternatively, the fixation device may be across-pin fixator, adapted to be received in a bone tunnel drilledtransverse to a bone tunnel for receiving the elongate member, thecross-pin fixator being adapted to be received though the aperture ofthe elongate element to secure the elongate element to the subject'sbone. In this case, said latching element is the part of the fixationdevice adapted for passing through the aperture of said elongate member.

According to a further aspect of the invention there is provided animplant device for implantation at a joint, the implant devicecomprising

-   -   a body portion having first and second ends, and    -   first and second elongate members, the first elongate member        extending from the first end of the body portion and the second        elongate member extending from the second end of the body        portion,    -   the implant device further having a reinforcing element that        extends through the first elongate member, through the body        portion of the implant device, and through the second elongate        member, the first and second elongate members being adapted for        fixation relative to a subject's body.

Suitably, the reinforcing element transfers forces exerted on the bodyportion of the device to the subject's body in use by means of theelongate members with reinforcing element therein being fixed to thesubject's body in use. The reinforcing element extends into the elongatemembers of the implant device, which are anchored to the body in use,therefore allowing the reinforcing element to transfer mechanical loadsexerted on the body portion of the implant during use to the subject'sbody. The reinforcing element is therefore a tension member. Suitablythe reinforcing element is embedded within a polymeric matrix that formsthe body portion. Suitably the reinforcing element is also embeddedwithin the polymeric matrix at each of the elongate members, thecross-section of the implant device being smaller in each elongatemember than that of the body portion. Suitably the reinforcing elementis unitary, in that it forms a single piece that extends through thelength of the device, from within the first elongate element, throughthe body portion, and into the second elongate element. The device mayhave more than one reinforcing element. Suitably the implant device hasfirst and second means for fixing the first and second elongate membersto the subject's bone respectively. The first and second elongatemembers may be adapted to be fixed to a subject's body directly orindirectly.

The implant device is used as a replacement for natural tissues,including for example, replacement of the menisci of the knee joint. Theimplant device has the ability to accurately mimic the mechanicalbehaviour of the native tissue. The implant device comprises a hybridmaterial having two or more constituents, which through theirgeometrical arrangement within the implant device are able to create aheterogeneous structure similar to those native tissues that it isdesigned to replace. The implant device is able to provide improvedbiomechanical behaviour compared to prior art implant devices.

Preferably the implant device includes fixing means for securing thefirst and second elongate members to a subject's body.

According to a further aspect of the invention there is provided animplant device for implantation at a joint, the implant devicecomprising a body portion having first and second ends, and

first and second elongate members, the first elongate member extendingfrom the first end of the body portion and the second elongate memberextending from the second end of the body portion,

the implant device being made from a functionally graded material,having at least one mechanical property that varies spatially withrespect to the implant device.

Preferably the body portion is substantially crescent shaped. Preferablythe implant device has at least one mechanical property that varies in aradial direction relative to the crescent shaped body portion and/or ina circumferential direction relative to the implant device.

The at least one mechanical property may for example be elastic modulus,tensile stress and/or shear stiffness.

Suitably, the implant device comprises a synthetic tissue with materialproperties that vary spatially within the device. The implant deviceexhibits a spatial graded change in the magnitude of one or morephysical property. The implant device may comprise a hybrid functionallygraded material comprising at least two material ingredients that arevaried geometrically in their arrangement to vary localised materialproperties. Freeform production processes may be used to manufacture theimplant device in order to produce a device having properties that varyspatially.

Suitably the form of the implant device replicates that of the nativetissue that it is designed to replace with the inclusion of one or morefixation adaptations to the device which assist or are capable ofachieving fixation relative to a subject's body.

The term ‘circumferential direction’ as used herein refers to adirection extending along the axis of the first elongate member, along apath substantially parallel with the circumference of the crescentshaped body portion, and along the axes of the first and second elongatemembers. Where the body portion is crescent shaped, the circumferentialdirection would be a curved axis, substantially parallel with the outerrim of the crescent shaped body portion.

Preferably the implant device further comprises a reinforcing elementthat extends through the first elongate member, through the body portionof the implant device, and through the second elongate member, the firstand second elongate members being adapted for fixation relative to asubject's body.

Preferably the reinforcing element is an elongate element.

Preferably the reinforcing element is strap shaped.

Preferably the body portion is substantially crescent shaped, having anarcuate outer rim. The crescent shaped body portion could also bedescribed as arc shaped or shaped like a segment of a circle, with thefirst and second elongate members extending from the end points

Preferably the reinforcing element extends along, or close to andsubstantially parallel with, the arcuate outer rim of the body portionof the device.

Preferably a planar face of the strap shaped reinforcing element issubstantially perpendicular to the transverse plane of the body portionof the device in use. The transverse plane of the device is parallelwith the transverse plane of the knee when it is implanted at the knee.

Preferably the implant device further comprises a structural elementcomprising a plurality of fibres embedded within the body portion.

Preferably at least a portion of each of the fibres extends through thebody portion.

Preferably each of the fibres extends through the first elongate member,through the body portion of the implant device, and through the secondelongate member.

Preferably each of the fibres is coupled to the reinforcing element atleast one point along the length of said fibre. Preferably each of thefibres is coupled to the reinforcing element at two or more points alongthe length of said fibre.

Preferably the plurality of fibres are arranged such that each fibrecrosses over at least one other fibre.

Preferably when the implant device is not subjected to any externalforces, the fibres are arranged substantially parallel with the arcuateouter rim of the body portion or, if straight, as chords of the circleformed by the outer rim of the body portion.

Preferably when the implant device is not subjected to any externalforces, at least a portion of each fibre is arranged in wave likeformation. The wave like arrangement of each fibre suitably has crestsand troughs.

Preferably at least a portion of each fibre extends between theposterior and anterior ends of the body portion in a sinusoidal shapedformation.

Preferably the plurality of fibres comprises at least one electrospunanisotropic polymer sheet.

Preferably the body portion is made of or includes a functionally gradedmaterial.

Preferably the body portion has an elastic modulus gradient, the elasticmodulus varying spatially within the body portion. For example, the bodyportion may be manufactured from two elastomers via a singular injectioncasting, producing a continuous gradient or transition of materialproperties.

Preferably the elastic modulus increases in a radial direction, towardsthe arcuate outer rim of the body portion.

Preferably the elastic modulus increases in a circumferential directiontowards free ends of the first and second elongate members.

Preferably the elastic modulus increases towards the outer surface ofthe body portion.

Preferably the body portion has a high tensile stiffness along an axissubstantially parallel with the outer rim of the body portion,preferably in the range to 50 MPa to 2 GPa and low shear stiffness in aplane substantially transverse to the outer rim of the body portion,preferably in the range 2 to 50 MPa. In other words, the body portionhas a low shear stiffness in a plane parallel with a radial axis of thebody portion.

Preferably the body portion has a higher tensile stiffness along an axissubstantially parallel with the outer rim of the body portion than theshear stiffness in a plane substantially transverse to the outer rim ofthe body portion.

Preferably the reinforcing element has at least one securing fibreanchored thereto and extending away from the body portion of the implantdevice. The securing fibres may be used to fix the body portion to thesubject, to provide additional fixation that may be temporary orpermanent. The securing fibres preferably emerge from the periphery ofthe body portion, to be used for surgical insertion and/or fixation. Thesecuring fibres may be formed into sutures, which may have needles orsoft tissue fixation devices such as toggles mounted on their ends, sothat, if implanting at the knee, the sutures may pull the implant deviceinto the back of the knee and then secure it against the capsule there.

Preferably the body portion has at least one area adapted for tissueingrowth. In order to encourage fixation of the body portion of theimplant device with the surrounding joint capsular tissues, at least aportion of the implant device may be provided with tissue ingrowthzones. For example, at least a portion of the implant device may beprovided with a textile like outer surface, for promoting soft tissueattachment. At least a portion of the implant device could be mouldedwith textiles, such as those used in arterial grafts and heart valves.The textile could, for example, have a looped structure, akin to velour,so that the loops on the inner side are moulded into or otherwiseadherent to the implant device, while the loops on the outer side willallow tissue ingrowth to the velour-like material. These tissue ingrowthzones may have variable extent, depending on which areas are desired tobe fixed to the surrounding tissues. For example, it is desirable thatsome zones remain unattached, to aid mobility during knee movements,while it is desired that tissue adhere to other zones. Suitably, themechanical behaviour of the implant device under load may promoteintegration via tissue growth between the device and biological tissuein certain zones and/or may reduce integration via tissue growth betweenthe device and biological tissue in other zones, for example in theentrances of the bone tunnels which accommodate the fixation means.Suitably a portion of the surface of the body portion may be adapted fortissue ingrowth, in order to stimulate peripheral fixation of thedevice.

Preferably the body portion has a top face and a bottom face, the topface being substantially concave and the bottom face being substantiallyflat or substantially concave. Where the implant device is forimplantation at the knee, the top face faces the femur when implantedand the bottom face faces the tibia when implanted. The cross-sectionalshape of the body portion may vary along a circumferential axis of thebody portion. In particular, the radius of curvature of the top face mayvary along a circumferential axis of the body portion.

According to a further aspect of the invention there is an implantsystem according to the first aspect of the invention described aboveincorporating an implant device having the features of the implantdevice according to further aspects of the invention.

Preferably the implant system is for implantation at a subject's kneejoint, one of the first and second elongate members being a posteriorinsertion for securing at a posterior region of the subject's tibia andthe other of the first and second elongate members being an anteriorinsertion for securing at an anterior region of the subject's tibia inuse. According to a further aspect of the invention, the implant systemis a prosthetic meniscus implant system.

A kit can be provided comprising an implant system having a set ofimplant devices according to any preceding claim wherein the implantdevices are provided in a range of sizes. This allows the device to beoptimised for the exact dimensions of the individual patient, byselecting the device that ensures optimal fit with the particularpatient. The devices can be provided with a set of rules that assist inselection of a suitable implant from the implant set based on thepatient's dimensions.

The system can be supplied with a detailed operative plan for thepositioning of bony attachments and tunnels, that can be achieved by theuse of patient specific drill guides, or the use of surgical navigationor robotic assistance.

According to a further aspect of the invention there is provided amethod of implanting an implant system in a subject, the methodcomprising

-   -   providing an implant system according to any of the previous        aspects of the invention,    -   securing the implant device of the implant system to a subject        at a first fixation point,    -   exerting a predetermined tension on the first elongate member,        -   engaging the at least one cooperating element of the first            elongate member with the at least one latching element of            the corresponding fixation device such that the first            elongate member can be secured to the subject at a            predetermined tension. The fixation device can be secured to            the subject before or after engaging the at least one            cooperating element with the latching element.

For example, the fixation device may be a cross-pin fixator or aninterference screw that passes through an aperture in the first elongatemember. The first elongate member may have a plurality of aperturesspaced along its length, such that the desired predetermined tension canbe achieved.

According to a further aspect of the invention there is provided amethod of implanting an implant system in a subject, the methodcomprising

-   -   providing an implant system according to any of the previous        aspects of the invention,    -   engaging the at least one cooperating element of the first        elongate member with the at least one latching element of the        corresponding fixation device, such that the first elongate        member and fixation device can move relative to one another in        one direction, but not in the opposite direction.

The method allows for improved fixation of the implant device tomaintain the ability of the implant device to transmitpressure/compressive loads to the subject's body. The fixation meansalso allows for optimised tensioning of the implant device duringimplantation and during subsequent revision procedures to re-tension theimplant device if desired.

According to a further aspect of the invention there is provided amethod of tensioning an implant device, the method comprising

-   -   providing an implant system according to any of the previous        aspects of the invention,    -   securing the implant device of the implant system to a subject        at a first fixation point,    -   engaging the at least one cooperating element of the first        elongate member with the at least one latching element of the        corresponding fixation device, such that the first elongate        member and fixation device can move relative to one another in        one direction, but not in the opposite direction, and    -   moving the elongate member relative to the fixation device to        tension the implant device.

Function of the implant device may depend on correct tensioning of theimplant device, such that it fits snugly around the contact area of thefemoral condyle and on the tibial plateau. Suitably, the implant deviceis fixed to the tibia at one fixation end and tensioning means areattached at the other fixation end of the implant device. Once theimplant device has been secured to the subject at the first fixationpoint, the elongate member extending from the other end of the implantdevice can be secured to a tensiometer and the tension adjusted toobtain a snug fit around the femoral condyle. The elongate member canthen be secured with this tense configuration. Suitably the method canbe used to tense and re-tense the implant device.

Features mentioned above with any aspect of the invention may be appliedin any combination to the other aspects of the invention, as thoseskilled in the art will appreciate.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be moreparticularly described by way of example only with reference to theaccompanying drawings, wherein:

FIG. 1 shows a perspective view of an implant device according to afirst embodiment;

FIG. 1A shows a close-up of the stepped top surface of the posteriorinsertion of the implant of FIG. 1;

FIG. 1B shows a close-up of the stepped top surface of the anteriorinsertion of the implant of FIG. 1;

FIG. 2 is a schematic diagram showing a perspective view of an implantdevice of the present invention, illustrating how gradients ofproperties of the device may be exhibited in the implant device;

FIG. 3 is a perspective view of an implant device, similar to theimplant device of FIG. 1, showing the body portion cutaway, revealing astrap, a structural element, a bulk matrix and an overmoulding;

FIG. 4 shows a perspective view of the body portion of an implantdevice; FIGS. 4A to 4C show perspective views of various embodiments ofthe body portion of the device of FIG. 4, showing the body portioncutaway to show the constituents of the hybrid functional gradedmaterial; FIG. 4A shows a body portion having an overmoulding, strap andstructural element comprising a plurality of fibres; FIG. 4B shows abody portion like that of the FIG. 4A embodiment, but without anovermoulding; FIG. 4C shows a body portion like that of the FIG. 4Bembodiment, but having cavities and without a plurality of fibres;

FIG. 5A shows a perspective view of an implant device, with the polymercore material not shown, showing the strap and the reinforcingstructure;

FIG. 5B shows a perspective view of a further embodiment of an implantdevice, like that of the FIG. 5A embodiment, but having a strap of wovenmaterial;

FIGS. 6A to 6F show perspective views of various embodiments of implantdevices, with the polymer core material not shown;

FIG. 7 shows a perspective view of an implant system incorporating animplant device of FIG. 1, shown implanted onto the tibial plateau of asubject, showing the posterior and anterior fixation means;

FIG. 8 shows a different perspective view of the system of FIG. 7, witha portion of the tibia shown cutaway to show how fixation of theposterior insertion is achieved;

FIG. 9 shows a close-up perspective view of an implant system similar tothat of FIG. 7, the system further including a sheath, the system shownimplanted onto the tibial plateau of a subject, a portion of the tibiashown cutaway to show how fixation of the posterior insertion isachieved;

FIG. 10A shows a perspective view of the anterior insertion of theembodiments of FIGS. 3, 5A or 6A to 6F, the anterior insertion having aplurality of pre-formed holes for mating with a screw fixator, to fixthe anterior insertion to the subject's tissue;

FIG. 10B shows a close-up view of the anterior insertion of the FIG. 10Aembodiment, showing the outer polymer core material cutaway, and showingthe strap that is embedded within the anterior insertion, with thepre-drilled holes extending through the polymer matrix and the strap.

FIG. 11 shows a cross-sectional close-up view along the posteriorinsertion of FIG. 7;

FIG. 12 shows a cross-sectional close-up view along the anteriorinsertion of FIG. 7;

FIG. 13 shows a perspective view of an implant device having a velourpatch on a portion of the surface of the outer rim of the body portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments represent currently the best ways known to theapplicant of putting the invention into practice. But they are not theonly ways in which this can be achieved. They are illustrated, and theywill now be described, by way of example only. Like reference numeralsrefer to like parts throughout the drawings.

Referring to FIG. 1, this shows an implant device 10 which may beimplanted at the knee as a meniscus prosthesis device. The implant has abody portion 20 shaped approximately as a crescent (i.e. arc shaped orshaped as a segment of a circle), with a substantially wedge shapedcross-sectional shape (i.e. with the outer rim of the body portion beingthicker than the inner rim), emulating the shape of natural meniscustissue in a healthy knee joint. The body portion 20 has a bottom, ortibial face (not visible in FIG. 1), which faces the tibia whenimplanted and a top, or femoral face 42, which faces the femur whenimplanted. The body portion 20 has a posterior end 15 and an anteriorend 16, corresponding to a subject's posterior and anterior respectivelywhen the implant device is implanted.

The bottom face of the body portion 20 may be substantially flat and thetop face 42 may be substantially concave. Alternatively, the bodyportion 20 may be biconcave (i.e. wherein both the bottom face and topface 42 are concave). In a preferred embodiment the cross-sectionalshape of the body portion 20 perpendicular to its transverse plane whenimplanted varies along the circumferential axis (i.e. thecross-sectional shape varies along an axis substantially parallel withthe outer rim of the body portion). In such an embodiment, the bottomface of the body portion 20 may be substantially flat except for aportion at the posterior end of the body portion 20, wherein the bottomface is concave. This embodiment may be particularly useful forreplacement of a subject's lateral meniscus. The radius of curvature ofthe concave top face 42 of the body portion 20 may also be greatertowards the posterior and anterior ends of the body portion.

A first elongate member 40 extends from the posterior end 15 and asecond elongate member 30 extends from the anterior end 16 of the bodyportion 20. The first elongate member is a posterior insertion 40 andthe second elongate member is an anterior insertion 30 of the implantdevice 10. The term ‘insertion’ is used herein to describe the posteriorand anterior elongate members, however another term that may be used forthese members is ‘posterior fixation’/‘anterior fixation’; it will ofcourse be understood that the elongate members need not be insertedthrough any bone tunnel or fixation device in order to secure theposterior and anterior elongate members to the subject, but can besecured to the subject using suitable fixing means. Preferably both theposterior and anterior insertions 40, 30 are flat elongate members, suchas a strap (i.e. like a belt or tape) or the like. Alternatively, theanterior and/or posterior insertions 30, 30 may be substantiallycrescent shaped in cross-section. The concave side of the crescentcross-sectioned portion of the insertion can be curved to substantiallycorrespond to curvature of a fixation device such as a screw, and theconvex side of the insertion can be shaped to fit against the curvedside wall of a tunnel in the subject's bone for receiving the insertion.

The tibial face and femoral face 42 of the body portion 2 are textured,for example with a plurality of indentations 21, which help to retainliquid from the surrounding area, providing improved lubrication betweenthe device and biological tissue. The texturing of the tibial andfemoral faces can also be used to emphasise and vary mechanicalproperties of the device in relation to the specific requirements in aparticular subject's knee joint.

The implant device 10 is a synthetic tissue, which is preferably ahybrid functionally graded material comprising two or more materials,which are geometrically arranged to try to mimic the locally anisotropicproperties of the naturally occurring meniscal tissue. Functionallygraded materials are so called because their properties have a spatialgradient. Referring to FIG. 2, this schematically shows four differentzones that the implant device may have, which have different mechanicalproperties. Although the schematic diagram in FIG. 2 marks the zones ashaving discrete boundaries, the boundaries between the zones may alsoexist as gradients. The implant device body portion 20 has a centralportion 11, extending from the inner rim of the body portion to near theouter rim, the central portion 11 being soft in order to conform todeformation from the load of the articular surfaces. The body portionhas a peripheral portion at its outer rim, which should be much stiffer,to prevent the central portion 11 from being displaced from thearticular surfaces. Extending from the posterior and anterior ends ofthe outer rim 12 are a posterior insertion portion 14 and anteriorinsertion portion 13. The posterior insertion portion 14 and anteriorinsertion portion 13 are exceptionally stiff, and are adapted to securethe device to bone, while allowing the device to biomechanicallysimulate the movement of the natural tissue.

The implant device 10 preferably features three-dimensional gradients ofelastic and shear moduli. The elastic modulus throughout the deviceshould approximate values measured in the natural meniscus, such asbetween 2 GPa and 2 MPa.

The three-dimensional gradient is created by arranging the constituentmaterials of the device such that when a localised volume is analysed asa whole, the general properties are close to or match those of a naturalmeniscus. The three dimensional gradient is made up of two materialgradients in order to try to mimic the behaviour of the meniscal tissue:a gradient in the radial direction of the crescent shaped implant deviceand a gradient in the direction of the circumference of the implantdevice (i.e. in a direction between posterior and interior insertions,including the arc between the posterior and anterior ends of the bodyportion). In the radial direction of the body portion 20, the centralportion 11 preferably has a bulk elastic modulus of around 10 MPa.However, the outer rim 12 should preferably remain stiff in order tostop the meniscal tissue from being displaced from the tibial plateau. Agradient preferably exists along a radial direction of the implant bodyportion from the outer rim 12 to the inner rim with the average elasticmodulus varying from values around or above 50 MPa at the outer rim toaround or lower than 2 MPa at the inner rim.

In a circumferential direction, gradients preferably occur where theload bearing body grades to each of the anterior and posterior insertionportions 13, 14. In a circumferential direction, the elastic modulusvaries from values of around or above 100 MPa within the anterior andposterior insertion portions 13, 14, to values as low as 10 MPa withinthe body portion 20.

The elastic modulus gradients are achieved through the uniquearrangement of constituent materials. Embedded within the implant devicemay be a reinforcement structure (such as a polymer structure, forexample made of polyetherketone (PEEK) or other high-modulus polymer).The reinforcement structure may vary in its structure along both thecircumference of the device and in a radial direction. Other polymers orpolymer substitutes may be used for the reinforcement structure, havingan elastic modulus within a range of around 80 MPa to 2 GPa.

The reinforcement structure is overmoulded with or embedded within apolymer, preferably an elastomer, which makes up the main bulk of thedevice. This polymer matrix making up the main bulk of the implantdevice may be a silicone/polyurethane elastomer (or elastomer substitutepreferably with an elastic modulus below around 10 MPa). The matrixpolymer may comprise a functionally graded material, manufactured tohave an elastic modulus that varies along the radial direction of thedevice, the circumferential direction of the device, or both.

The polymer matrix core of the implant device may also have anovermoulding of another polymer (preferably an elastomer) withappropriate wear characteristics to form the outer surface of theimplant device, for example poly carbonate urethane. The overmouldingcan either be carried out as a one or two stage process depending onwhether a continuous or discontinuous gradient between materials is tobe achieved.

An example of how these elastic modulus gradients can be achieved isshown in an embodiment of FIG. 3, which shows a cutaway through animplant device 100 revealing the hybrid functionally graded material(FGM) structure. The implant device 10 has an outer overmoulding 25 onthe surface of the device, made of a super wear-resistant elastomer.Within the overmoulding 25 is a soft elastomer/elastomer foam core 24,which makes up the bulk of the body portion 20 of the device. In FIG. 3,the overmoulding 25 and core 24 are shown cutaway, revealing areinforcement structure 22, 23 embedded within the core 24. The core 24effectively forms a matrix in which the reinforcement structure islocated. The reinforcement structure is made up of two components. Thefirst component is a strap 22, which runs continuously through theanterior insertion 30, through the outer rim of the body portion 20 andthen through the posterior insertion 40 of the device. The strap 22 ismade of a material having a high elastic modulus. The strap 22 is a flatpiece of stiff yet flexible polymer (such as PEEK or polyethylene), suchas a piece of polymeric ribbon or tape. Alternatively the strap 22 maybe moulded with a woven or braided fibre structure within it. The secondcomponent of the reinforcement structure is a further structural element23, preferably located within the central portion 11 portion of the bodyportion 20, different examples of which will be further described below.In the FIG. 3 embodiment, the structural element 23 is shown as asinusoidal arrangement of fibres. The fibres are preferably polymerfibres, and will be described in more detail below. The structuralelement 23 may be affixed to, integral with, or separate from the strap22. The fibres of the structural element 23 may extend from the bodyportion 20 into both the anterior insertion 30 and posterior insertion40. The polymer core 24 may extend from the body portion 20 to theanterior and posterior insertions 30, 40. The overmoulding 25 may bepresent, on the anterior and posterior insertions 30, 40, as well as onthe body portion 20.

Referring to FIGS. 4 and 4A to 4C, further embodiments of an FGMstructure are shown. FIGS. 4A to 4C show cutaway sections showing detailof possible embodiments of the body portion 20 of the implant device 200shown in FIG. 4. FIGS. 4A to 4C show cross-sections through the bodyportion of each embodiment along a radial direction. Referring to FIG.4A, this shows a body portion 20, which as with the FIG. 3 embodiment,has an overmoulding 25 of a wear-resistant elastomer. Within theovermoulding 25, the main bulk of the body portion 20 is comprised of acore 24. Embedded within the core 24 is a strap 22, which as with thestrap 22 in the FIG. 3 embodiment, runs continuously through theanterior insertion 30, through the outer rim of the body portion 20,very close to the outer rim, and then through the posterior insertion 40of the device. Also embedded within the core 24 is a structural element23A, comprising elongate fibres. The structural element 23A extendsthrough the body portion 20, along a circumferential direction, and islocated within the body portion 20, radially between the strap 22 andthe inner rim of the body portion 20. The fibres may be randomlyarranged, as in the FIG. 6A embodiment described below.

FIG. 4B shows an embodiment like that of FIG. 4A, except that theimplant device does not have any overmoulding layer over the core 24. Anovermoulding layer may not be needed if an elastomer/foam withsufficiently low elastic modulus yet high enough wear-rate constant isused for the material of the core 24, or if the core 24 is made of twoelastomers as a single injection casting producing a continuous gradientof material between the outer surface and the inner body for example.

FIG. 4C shows a further embodiment of a body portion. Like the FIGS. 4Aand 4B embodiments, the device has a strap 22 extending therethrough,parallel with the outer rim of the body portion 20. In the FIG. 4Cembodiment a much higher elastic modulus material with sufficient wearresistance is used as the material of the core 24. One or more cavities27 are provided within the core 24 to provide radial elastic or shearmodulus values similar to the tissues of a natural meniscus. Thecavities 27 may be empty (i.e. voids in the material of the core 24) ormay contain a low elastic modulus material. The embodiment shown in FIG.4C has two cavities, which extend in a circumferential direction throughthe body portion 20.

Referring to FIG. 5A, this shows a further embodiment of an implantdevice 300. As with the previous embodiments, a single integral strap 22continuously extends from the posterior insertion 40, through the bodyportion 20, and into the anterior insertion 30. The strap 22 providesanchoring points for sutures 50 that exit out of the device body. Thesutures 50 may be used to secure the device to surrounding soft tissues.The sutures 50 and structural element 23B may be fabricated as part ofthe strap 22 or joined to the strap 22 through chemical or mechanicalfixation. The sutures 50 may be pre-woven threads to be used as guidewires to assist in the implantation of the implant device duringsurgery. Alternatively, the implant device may have fixation points forsuturing which are designed such that the material of the body portionis pierced and sutures or the like are threaded through said pointsbefore being attached to surrounding tissue.

The strap 22 additionally provides an anchoring point for a furtherstructural element 23B located in the body portion 20. The structuralelement 23B is comprised of a plurality of polymer fibres 35. Each fibre35 is coupled to the strap 22 at one or more attachment points 36.Preferably each fibre 35 is coupled to the strap 22 at two attachmentpoints 36, first and second attachment points of each fibre being spacedapart from one another along the length the strap 22. The path of eachfibre 35 between first and second attachment points 36 (e.g. betweenattachments points 36 a and 36 b shown in FIG. 5A) provides a tangentline, the plurality of tangent lines provided by the plurality of fibreseffectively providing a curved inner rim 36 c of the structural element23B. This arrangement of fibres creates a high concentration of fibresat the inner rim of the body portion 20, this being an area of themeniscus that is prone to tearing. This arrangement of fibres thereforehelps prevent the implant device from becoming torn at the inner rim.The structural element 23B therefore provides shearing stiffness to theimplant substantially within the plane of the body portion 20. All orsome of the fibres are pre-tensioned between the attachment points.Alternatively, the fibres are not pre-tensioned but are substantiallyslack between attachment points.

Each attachment point of a particular fibre may be at the same height onthe strap 22 (relative to the top and bottom edges of the strap 22).Alternatively, the attachment points of a particular fibre may be atdifferent heights on the strap. By arranging the fibres such that someattachment points are at or near the top edge of the strap and someattachment points are at or near the bottom edge of the strap and/orsome attachment points are at locations between the top and bottom edgesof the strap, the fibres 35 provide a reinforcement structure 23B thatspans the depth of the body portion 20 between the tibial face andfemoral face of the implant device.

Each of the fibres 35 preferably crosses at least one other fibre of thestructural element 23B.

The fibres 35 are gathered together such that they extend close to oneanother at the posterior and anterior ends of the body portion 20, suchthat there is a high density of fibres where the body portion 20 extendsinto the posterior and anterior insertions 40, 30 of the device. Thefibres 35 may extend substantially along the whole of or a portion ofthe length of the posterior and anterior insertions 40, 30.

As the body portion 20 of the implant device is compressed by the femurduring use, the wedged cross-section of the body portion 20 will becaused to extrude radially, causing the circumference of the device toincrease. These compressive loads are transferred into circumferentialor “hoop” stresses; tension within the body portion 20 is transferredvia the strap 22, into the posterior and anterior insertions 40, 30. Theposterior and interior insertions 40, 30 will be fixed to the subject'stissue (as will be described below), therefore the strap 22 transfersforces within the implant device to the subject's tissue. Compressiveloads on the implant are also transferred to the fibres 35 of thestructural element 23 b, any slack between the attachment points of eachfibre absorbing the tensile forces. As the body portion 20 stretches,the fibres 35 get closer to one another, the crossovers between thefibres causing the structural element 23 b to increase in stiffness asit is stretched.

The fibres 35 may be threadedly coupled to the strap 22 to form eachattachment point 36 (e.g. by sewing). Alternatively the fibres 35 may beadhered to the strap 22 at each attachment point 36, for example usingglue.

Instead of having single fibres that are affixed to the strap 22 at oneor more attachment points, each fibre may be comprised of more than oneconstituent fibre, each constituent fibre terminating at an attachmentpoint with the strap 22. The constituent fibres transfer forces exertedon the fibres to the strap 22, which transfers forces from the bodyportion 20, to the anterior and posterior insertions 30, 40, and to thesubject's tissue, via fixation of the anterior and posterior insertions30, 40, and to the subject's tissue.

The strap 22 and structural element 23B are embedded within thepolymeric material of the core (not shown in FIG. 5A).

Referring to FIG. 5B, this shows a further embodiment of an implantdevice 400 like that of the FIG. 5A embodiment, but wherein the strap 22b is formed of woven extruded fibres. The fibres of the strap 22 b maybe woven in any suitable arrangement. The outer material of the anteriorinsertion 30 is not shown, such that the woven strap 22 b that extendsfrom the body portion 20 and into the anterior insertion 30 is visiblein the anterior insertion 30. The strap 22 b also extends from the bodyportion 20 into the posterior insertion 40, however in FIG. 5B, theouter material of the posterior insertion 40 is shown, such that thestrap 22 b is not visible in the posterior insertion 40.

The strap 22 b of the implant device 400 in the FIG. 5B embodiment ismade from woven fibres, however it will be understood that the strapcould be made from a combination of solid and woven elements.

FIG. 6A to 6F show further embodiments of implant devices, each having adifferent form of structural element 23 comprising fibres, the fibres ofthe structural element 23 each having a different geometry/arrangementin each embodiment. Each of the embodiments 6A to 6F has a strap 22,like in the previous embodiments, which extends through the posteriorinsertion 40, body portion 20 and anterior insertion 30. As a result,the anterior and posterior insertions can be as stiff as possible inaxial tension, while also remaining soft enough for a surgeon to bendthem and thread them through a tunnel or channel for the purposes offixation (as described below). In each of FIGS. 6A to 6E, the structuralelement that is provided in addition to the strap 22 is comprised of aplurality of polymer fibres, which may vary in thickness from 1 μm to 1mm. In FIGS. 6A to 6F, the strap 22 and structural element are embeddedwithin a polymeric material (not shown in the figures). All of theimplant devices of the FIG. 6A to 6F embodiments can be made by rapidprototyping.

The FIG. 6A embodiment is an implant device 500 having a structuralelement 23A wherein the polymer fibres 35 are substantially randomlyarranged. Preferably, the fibres 35 are not coupled to the strap 22. Thefibres extend along a direction substantially parallel with the outerrim of the body portion, the fibres crossing over one another along thecircumferential path. The fibres are arranged such that each fibrecrosses over at least one other fibre. The fibres may extend into theposterior and anterior insertions 40, 30 or may terminate where by thebody portion 20 transitions to the posterior and anterior insertions 40,30. The fibres are designed to be loose when encapsulated, only drawingtight and affecting the elastic modulus of the implant device when thedevice has undergone a certain level of strain. The criss-crossingfibres in the structural element 23A may be glued together. The fibresin the FIGS. 4A and 4B embodiments may be arranged as in the FIG. 6Aembodiment.

The FIG. 6B embodiment is an implant device 300 wherein the structuralelement 23 b is formed as in the FIG. 5A embodiment, as described above.

The FIG. 6C embodiment is an implant device 600 that has a structuralelement 23C which is similar to the structural element 23B of the FIG.6B embodiment, except that the fibres 35 are each coupled to the strap22 at more attachment points 36 than in the FIG. 6B embodiment. Eachfibre 35 is preferably coupled to the strap at around four attachmentpoints 36, the attachment points 36 of each fibre being spaced along thelength of the strap 22 (of course, the fibres could have more or lessattachment points). The fibres have axial stiffness against elongation,but are transversely flexible. This arrangement provides a more rigidreinforcing structure than that of the arrangement of fibres in thestructural element 23B in the FIG. 6B embodiment. The FIG. 6C structuralelement 23C has a reinforcing structure involving a cellular structure.By varying elements such as the fibre diameters, the cell sizes or theoverall arrangement of fibres, it is possible to design a structure thatcan elastically deform and reinforce the inner rim of the device. Someof the reinforcing fibres are attached at or close to the upper rim ofthe outer circumference (e.g. at attachment point 601), while othersattach at or near to the lower surface of strap 22 (e.g. at attachmentpoint 602), thus giving a volume of material with fibre reinforcementwhich has a substantially triangular cross-section, reinforcing close tothe upper and lower surfaces of the body, thus protecting the surfacesagainst tearing.

The FIG. 6D embodiment is an implant device 700 that has a structuralelement 23D comprising a plurality of fibres that are each arranged in awavelike configuration (e.g. a sinusoidal configuration). The fibres arenot under tension when encapsulated in the polymeric matrix of the bodyportion 20, but can draw tight when the implant device is subjected totensile forces along a circumferential direction of the device. Thesinusoidally arranged fibres may cross over one another. Variation infrequency and orientation of the fibres can be used to affect theproperties of the implant device. The sinusoidal arrangement of thefibres gives this implant device embodiment a greater elasticity in thecircumferential direction than the other embodiments of FIGS. 6A to 6C.Once implanted, the body portion 20 of the device of the FIG. 6Dembodiment can be tensioned using attachment means, as described below,to optimise the elasticity of the device for the subject.

The FIG. 6E embodiment is an implant device 800 that has a structuralelement 23E made of a three-dimensional woven, braided or knittedstructure, which can be constructed or laminated into the body portion20 of the device. The woven structure 23E can stretch radially andcircumferentially, as the implant device is subjected to forces duringuse.

The FIG. 6F embodiment is an implant device 900 that has a structuralelement 23F comprising electrospun anisotropic polymer sheets that havebeen folded or laminated into the body portion 20 of the device. Thepolymer sheets may comprise a plurality of fibres that have been formedinto a polymer sheet via the electrospinning process. Control of theelectrospinning process enables variations in the fibre orientation tobe made throughout each sheet and can be used to control the anisotropythroughout the body portion 20 of the device.

In all of the embodiments shown in FIGS. 6A to 6F, the density of fibreswith respect to the body portion volume can be varied in order to varythe properties of the device such as the overall elasticity.

In all of the embodiments described above having a plurality of fibres,the reinforcing fibres can be condensed together within the bodyportion, as they approach the posterior and anterior ends of the bodyportion, such that there is a high density of fibres where the bodyportion 20 extends into the posterior and anterior insertions 40, 30 ofthe device, to increase the stiffness in this portion of the implant. Inthis way, the anterior and posterior insertions can be relatively stiffin axial tension, while also remaining soft enough for a surgeon to bendthem and thread them through a fixation tunnel or channel as describedbelow. The fibres 35 may extend within all or a portion of the length ofthe posterior and anterior insertions 40, 30.

Referring to FIGS. 1, 7 and 8, possible means for fixation of the deviceat a subject's joint will now be described. Referring to FIG. 1, theposterior insertion 40 has a stepped top surface 41 (i.e. a serrated orbarbed top surface). This stepped top surface 41 forms a plurality ofratchet elements being ratchet teeth 41 a on the posterior insertion 40.Referring to FIG. 1A, which shows a close up of the stepped surface 41,each ratchet tooth 41 a has a first surface 41 b that slopes downtowards the posterior insertion 40 in a direction towards the free endof the posterior insertion 40, and a second shorter surface 41 c whichslopes towards the posterior insertion 40 in a direction away from thefree end of the posterior insertion 40, the second surface having asteeper slope than said first surface. The plurality of elements on theposterior insertion 40 for cooperating with corresponding elements onthe fixation device (as will be described below) need not beassymetrical teeth, but could of course be any elements, such as thoseof a symmetrical screw thread form, that will engage in use with one ormore corresponding elements on a fixation device.

Referring to FIG. 7, this shows the implant device 10 of an implantsystem fixed to a tibia 60. The implant device 10 in FIG. 7 is showninstalled to replace the lateral meniscus of the knee joint. FIG. 7shows the relative location of cartilage 61 on the tibial plateaurelative to the installed implant device. The posterior insertion 41 isinserted during installation through a tunnel 80 that has beenpre-drilled in the subject's tibia 60. The tunnel 80 may be createdusing a suitable drill guide instrument. The tunnel 80 extends from anopening within the knee, in the posterior of the tibia to an opening ina wide anterior region 81 on the lateral side of the tibia, below thetibial plateau. An interference screw 90 or other suitable fixationdevice is used to fix the posterior insertion 40 in the tunnel 80. Theinterference screw preferably has external threading which is adapted topenetrate into bone on either side of the tunnel 80, fixing theinterference screw 90 in the tunnel 80 while, at its other side,interlocking with the serrated surface 41 of the posterior insertion 40.

FIG. 8 shows an alternative view of the posterior fixation through acutaway of the tibia 60 showing interference screw 90 mated against thestepped surface 41 of the posterior insertion 40. FIG. 11 shows aclose-up cross-sectional view through tunnel 80 in the tibia 60, showinghow the interference screw 90 mates against the stepped surface 41 ofthe posterior insertion 40 (only a portion of the posterior insertion40, adjacent its free end is shown in FIG. 11). In FIG. 11, theposterior insertion 40 has sutures 44 attached at its free end, for usein pulling the posterior insertion 40 down the tunnel 80 duringinstallation.

Referring to FIG. 1, the anterior insertion 30 has a stepped top surface31. This stepped top surface 31 forms a plurality of ratchet elementsbeing ratchet teeth 31 a on the posterior insertion 30. Referring toFIG. 1B, which shows a close up of the stepped surface 31, each ratchettooth 31 a has a first surface 31 b that slopes down towards theposterior insertion 30 in a direction towards the free end of theposterior insertion 30, and a second shorter surface 31 c which slopestowards the posterior insertion 30 in a direction away from the free endof the posterior insertion 30, the second surface having a steeper slopethan said first surface.

Referring to FIG. 7, the implant system has a low profile anteriorfixation plate 70 to fix the anterior insertion 30 to the tibia. Theanterior insertion 30 is strap shaped, akin to a tape, to avoid beingprominent where it passes out of the knee. The fixation plate 70 may bescrewed or stapled to the bone and is shaped to bridge over the anteriorinsertion 30 when implanted. For example, the fixation plate 70 may haveholes (not shown in the figures), one on each side of the bridgingcrossbar section, each for receiving a screw to pass through the screwhole and into the bone. The bridging crossbar section forms a channelunderneath the fixation plate through which the anterior insertion canbe received, when the fixation plate is affixed to the bone. When thefixation plate 70 is fixed to the tibia 60, there is a channel formedbetween the fixation plate 70 and the bone, the channel having a firstopen end 70 a, facing the body portion 20 of the implant device wheninstalled and a second open end 70 b, facing away from body portion 20of the implant device when installed. The fixation plate 70 has at leastone protuberance (not shown in FIG. 7) extending from the underside ofthe crossbar of the fixation plate 70 (e.g. a serrated underside) toengage the ratchet teeth of the anterior insertion 30 in use. Thefixation plate 70 therefore acts as a ratchet, allowing the anteriorinsertion 30 to be drawn through the channel formed underneath thecrossbar of the fixation plate 70, in a direction away from the bodyportion 20 of the implant device, when the fixation plate 70 is fixed tothe bone. However, the ratchet mechanism provided by the fixation plate70 prevents the anterior insertion 30 from being withdrawn from thefixation plate 70 in a direction towards the body portion of the implantdevice when installed.

FIG. 12 shows a cross-sectional view through the anterior insertion 30of FIG. 7, along the elongate axis of the anterior insertion 30 showinghow latching elements on the underside of the fixation plate 70 engagewith corresponding cooperating elements on the anterior insertion 30.The underside of the fixation plate 70 has a serrated surface, theserrations corresponding to the shape of the stepped surface 31 of theanterior insertion 30. The serrated underside 71 of fixation plate 70mates in use against the stepped surface 31 of the anterior insertion 30(only a portion of the anterior insertion 30, adjacent its free end, andonly a portion of tibia 60 is shown in FIG. 12). This provides a ratchetmechanism allowing the anterior insertion 30 to be drawn through thechannel formed underneath the crossbar of the fixation plate 70, in adirection away from the body portion 20 of the implant device butpreventing the anterior insertion 30 from being withdrawn from thefixation plate 70 in a direction towards the body portion of the implantdevice when installed.

During installation of the implant device, firstly a tunnel 80 isdrilled in the subject's tibia, the tunnel extending from an opening inthe posterior of the tibia to an opening in a wide anterior region 81 onthe lateral side of the tibia. The posterior insertion 40 is passed intothe knee through a small arthroscopy portal, and then passed around andunder the femoral condyle, and then inserted in the tunnel 80 via theposterior opening of the tunnel 80. The posterior insertion 40 ispreferably sized such that its free end extends out of the anterioropening of the tunnel 80 when the posterior insertion 40 is fullyinserted in the tunnel 80. Alternatively, the posterior insertion 40 ispreferably sized such that its free end is at/near the anterior openingof the tunnel 80 when the posterior insertion 40 is full inserted in thetunnel 80. The posterior insertion helps to pull the body portion intothe knee, and around the femoral condyle. The interference screw 90 isinserted in the anterior opening of the tunnel 80 such that it engageswith the posterior insertion 40, as shown in FIG. 7. The interferencescrew 90 also engages with the tunnel wall, creating a mechanicalfixing, fixing the screw 90 and posterior insertion 40 relative to thetunnel. When the posterior insertion 40 has been inserted in the tunnel80, the ratchet teeth 41 a of the posterior insertion 40 allow thethreaded screw 90 to be inserted from the anterior opening of thetunnel, but the ratchet teeth 41 a resist the posterior insertion frombeing withdrawn from the tunnel 80 via the posterior opening of thetunnel 80, by means of the ratchet teeth 41 a engaging with the threadsof the fixed interference screw 90. The ratchet teeth 41 a and theengagement of the interference screw 90 in the bone prevent the screw 90from being withdrawn from the tunnel 80 via the anterior opening.

Once the posterior insertion 40 has been fixed to the subject's bone,the anterior insertion 30 is fixed to the subject's bone using thefixation plate 70. The fixation plate 70 is fixed to the bone viasuitable means as described above (e.g. using screws or staples). Thefree end of the anterior insertion 30 can be inserted into the channelformed under the fixation plate 70 via the first open end 70 a, andpushed under the fixation plate 70 until the free end of the anteriorinsertion 30 exits via the second open end 70 b. Once the free end ofthe anterior insertion 30 is accessible, the free end can be pulledthrough the channel of the fixation plate. Alternatively, the anteriorinsertion 30 can be pushed through the channel of the fixation plate,the anterior insertion 30 being sufficiently stiff to be pushed throughwithout buckling. The ratchet mechanism formed between the steppedsurface 31 of the anterior insertion 30 and the fixation plate allowsthe anterior insertion to be drawn through the channel under thefixation plate in a direction facing away from the body portion 20 ofthe implant device, but prevents the anterior insertion from beingwithdrawn from the fixation plate in a direction towards the bodyportion 20 of the implant device. The ratchet mechanism thereforeprevents the anterior insertion 30 from detaching from the subject'sbone.

The fixation means for the anterior insertion therefore may additionallyact as a ratchet allowing tensioning once the posterior insertion isfixed. Once the posterior insertion 40 has been secured as describedabove, the anterior insertion 30 can be secured to a tensiometer and thetension adjusted to obtain a snug fit around the femoral condyle. Theanterior insertion will stop being drawn through the fixation plate bythe surgeon once the desired tensed configuration has been achieved. Theanterior insertion 30 will initially comprise sufficient length suchthat the free end of the anterior insertion 30 is easily accessible onceit has passed through the channel of the fixation plate. The anteriorinsertion 30 preferably comprises excess length in order to allowcorrect tightening of the device during implantation. Any excess lengthof the anterior insertion 30 can be cut away once the desiredfixation/tension has been achieved. Whereas the anterior insertion 30 ofthe implant device shown in FIG. 1 has a rounded free end, the free endof the anterior insertion shown in FIG. 7 has a square end, the excesslength of the anterior insertion having been cut away.

As shown in FIG. 11, either or both of the posterior and anteriorinsertions may have sutures 44 attached to the free end (e.g. in theform of a loop or tape), made of strong material. The sutures mayprotrude from the end of the moulding of the posterior and/or anteriorinsertion. The sutures aid implantation by providing something that thesurgeon can grasp and pull when implanting, for example being useful inpulling the posterior insertion 40 through the bone tunnel. The sutures44 are suitably thin and soft, for easy handling/knot tying.

Once the posterior and anterior insertions 40, 30 have been fixed to thesubject, if the installer wishes to increase the tension within theimplant device, the installer can draw the anterior insertion 30 furtherthrough the channel of the fixation plate, by pushing the anteriorinsertion, of pulling on the free end of the anterior insertion 30,until the desired tension has been achieved. It is desirable toinitially install the implant device such that it is not over-tense.Subsequently, if it is desired to increase the tension in the device, orthe implant device has become loose over time, the ratchet mechanismprovided by the fixation plate can be used to increase the tension onthe device.

Preferably the interference screw 90 will have external helical threads,which help the screw to engage with the bone of the tunnel 80 wall.However, it will be understood that the screw may have suitableprotuberances, other than helical threads, to engage with the steppedsurface 41 of the posterior insertion 40.

The posterior insertion 40 may be moulded with stiffer reinforcements,at least at the portion where it is intended to engage with theinterference screw 90. For example, the posterior insertion may bereinforced by the extension of the fibres of the structural element 23,23A, 23B, 23C, 23D, 23E, 23F from the body portion of the implant deviceinto the posterior insertion 40, reaching the portion of the posteriorinsertion that is intended to engage with the interference screw 90.

In addition to the use of the stepped surface 41 and interference screw90 to secure the posterior insertion 40 to the subject's bone, theposterior insertion may also include a plurality of holes through theposterior insertion (not shown in the figures), one of which could beengaged by a screw or cross-pin passing through, into the bone at one orboth sides.

When the implant device 10 is fixed as described above, the body portion20 of the implant device remains relatively free, much like the naturalmeniscus, with its fixation occurring at the extremes of the insertions30,40. The fixation means for the anterior insertion 30 effectivelysecures the anterior insertion to the tibial plateau, recognising thatthe anterior attachment is close to the anterior edge of the tibialplateau in the natural meniscus.

Referring to FIG. 9, this shows an alternative posterior fixation meansfor the implant device 10. In FIG. 9, the anterior end of the bodyportion 20 of the implant device is shown cutaway to show thecross-sectional shape of the body portion. FIG. 9 shows a cutawaythrough the tibia 60, showing a sheath 100 having been inserted in thetunnel 80. The sheath 100 is used in order to allow for easy exchange ofthe implant device without the need for re-drilling, for example if thematerial of the implant device has worn away.

The sheath 100 is a hollow, elongate member that is tubular in shape. Inthe FIG. 9 embodiment, the sheath has expanding ends 101 at each end ofthe sheath (although it will be understood that a sheath withoutexpanding ends could be used). In this embodiment, each end of thesheath 100 has two or more longitudinal cuts, the cuts preferably beingspaced around the circumference of the sheath. The cuts are of anappropriate length to allow the ends 101 of the sheath to flare/expand.The sheath 100 preferably has a length that roughly matches the lengthof the tunnel 80. When the sheath 100 is inserted in the tunnel 80, theexpanded ends 101 of the sheath 101 push against the cortical bone nearthe tunnel apertures (rather than pushing against the soft cancellousbone towards the mid-section of the tunnel 80). The expanded ends of thesheath 101 are caused to flare apart at the top, by pulling of thetapered posterior insertion 40 into the sheath 100, and at the bottomend by the insertion of screw 90.

The sheath 100 may have an outer surface texture and/or bioactivecoatings (such as hydroxyapatite) to promote bone ingrowth. The sheath100 may have a threaded internal surface matching that of theinterference screw 90.

During installation, the sheath 100 is inserted in a tunnel 80 that hasbeen pre-drilled in the subject's tibia. Preferably the sheath 100 isinserted from the anterior tunnel aperture, the ends 101 expanding inuse. The ends 101 expand against the cortical bone near the tunnelentrances, fixing the sheath against the bone. The posterior insertion40 is inserted in the tunnel 80 via the sheath end at the posterior ofthe tibia. The interference screw 90 is inserted in the end of thesheath at the anterior of the tibia and engages with the internal sheathwall, creating a mechanical fixing, fixing the screw and posteriorinsertion relative to the sheath, which is in turn fixed relative to thebone. In embodiments in which the sheath 100 has internal threadingmatching that of the interference screw 90, this helps lodge the screw90 within the sheath 100.

Referring to FIG. 10A, this shows an alternative embodiment of theanterior insertion 30′, like that shown in FIGS. 5A and 6A to 6F.Instead of having a stepped top surface 31, the anterior insertion 30′has a plurality of apertures 32 regularly spaced along its length. Ascrew fixing (not shown) can be used to directly fix the anteriorinsertion to the outer surface of a subject's tibia. Duringinstallation, once the posterior insertion has been fixed, tension willbe applied to the anterior insertion 30 until the implant device is at adesired tension, and a screw fixing (or other suitable fixing) will bepassed through one of the apertures 32, and driven into the subject'stibia. For example, a cortical screw could be used as the fixing, to fixthe anterior insertion to the anterior edge of the subject's tibialplateau. By providing a plurality of apertures 32, the installer caninsert the screw fixing into an aperture 32 that overlies a suitablepart of the subject's tibia to drive the screw fixing into, once theimplant device has been extended to its desired tension. In thisembodiment, the anterior insertion is therefore directly fixed to thesubject's tissue. Similarly, the posterior insertion 40, instead ofhaving a stepped top surface 41, may have a plurality of apertures (notshown in the figures), regularly spaced along its length. A screw orother suitable fixing could be used to directly fix the posteriorinsertion 40 to the subject's body. By providing a plurality ofapertures along the length of the anterior and/or posterior insertions30, 40, a desired tension can be exerted on the implant device wheninstalled.

In an alternative means for fixation of the anterior insertion shown inFIG. 10A, a fixation plate may be used (not shown in the figures). Aswith the FIG. 7 embodiment, the fixation plate has a bridging crossbarsection and side portions, each of which can be fixed to the subject'stibia via suitable fixation means (such as screws or staples). Thebridging crossbar section forms a channel underneath the fixation platethrough which the anterior insertion can be inserted, when the fixationplate is affixed to the bone. The fixation plate may be similar to thatof the FIG. 7 embodiment, except that it has a spike or tooth extendingfrom the underside of the crossbar of the fixation plate, adapted andshaped to engage with the apertures 32 in the anterior insertion 32. Thespike or tooth may be angled relative to the direction of insertion ofanterior portion 30′ such that the fixation plate and anterior portion30′ with plurality of holes acts as a ratchet, allowing the anteriorinsertion 30′ to be drawn through the channel formed underneath thecrossbar of the fixation plate in a direction facing away from the bodyportion of the implant, but with engagement of the spike or tooth of thefixation plate 70 in one of the holes of the anterior insertion 30′preventing the anterior insertion 30′ from being withdrawn from thefixation plate 70 in a direction towards the body portion of the implantdevice when installed. In this way, once the implant device has beeninstalled in place on a subject's tibia, and its posterior and anteriorends fixed to the bone, if the installer wishes to increase the tensionon the implant device, the installer can pull on the free end of theanterior insertion 30′, drawing the apertured anterior insertion throughthe ratchet-like mechanism of the fixation plate until the desiredtension is achieved.

FIG. 10B shows a close-up view of the anterior insertion 30′ of FIG.10A, showing the core material 24 that encases the strap 22 partiallycutaway, and showing the strap 22 that is embedded within. The apertures32 extend through the core material 24 and the strap 22, to providemaximum transfer of the shear forces from the implant device to thebone. Where a screw or similar fixing is used to directly fix theanterior insertion 30 to the bone, mitigation of stress concentration isachieved between the screw fixing (not shown) and the implant device.The reinforcing fibres (as described above in relation to FIGS. 3-6) maybe arranged to encircle the holes, thus strengthening them.

In an alternative means for fixation of the anterior insertion, a tunnelmay be drilled for securably receiving the anterior insertion 30, thetunnel being similar to the tunnel 80 for the posterior insertion shownin FIG. 7, also exiting the tibia below the tibia plateau. The anteriorinsertion will be secured to the tunnel similarly to the posteriorinsertion in the FIG. 7 embodiment. In embodiments where both theposterior and anterior insertions pass through bone tunnels to similarplaces on the surface of the tibia, then the two ends of the anteriorand posterior insertions may be folded over each other and secured by asingle fixation means, such as a buckle or staple, onto the surface ofthe tibia. The fixation means may include two sets of ratchet means, onefor engaging a stepped surface 31 of the anterior insertion 30 and onefor engaging a stepped surface 41 of the posterior insertion 40, fortensioning the anterior and posterior insertions relative to thefixation means in use. The ratchet means may be ratchet-like teeth onthe underside of the buckle, the sloping surfaces of each ratchet meansfacing in opposite directions.

FIG. 13 shows an implant device 10, with the body portion of the deviceinstalled on a subject's tibia 60, the implant device 10 having a velourpatch 72 located on a portion of the surface of its outer rim. Thevelour patch 72 provides a tissue ingrowth zone for peripheral fixationof the device. This allows the implant device to attach to the medialcollateral ligament for example.

The function of the meniscus implant depends on the location of thefixation to the tibia. Detailed coordinates of recommended attachmentpoints for the implant device can be provided, in relation toarthroscopically-identifiable bony landmarks, and similar dimensionswhich could be used in a surgical navigation or robotically-guidedsystem. These dimensions will inform the design of ‘offset’ drill guidesakin to those used in ligament surgery, such that the guide locates onthe prominent bony landmark and the guide ensures that the tunnel forthe meniscus fixation is positioned at the correct offset away from it,in the anatomical attachment area.

Before installation of an implant device as described herein theinstaller/surgeon must initially decide on the correct implant size touse. The implant devices described herein can be manufactured in a rangeof sizes. The implant devices can be supplied in a kit including a rangeof sizes to select from. Alternatively, the implant device can becustom-designed for a particular subject using MRI-based CAD-CAM. Thiscan be done for example by modifying the size in one or more dimensions.The implant device can be supplied with a patient specific implantationplan, for implementation using surgical navigation, robotic assistanceor patient specific drill guides.

In all of the embodiments described herein the strap 22, 22B can extendthrough substantially the full circumferential length of the implantdevice (i.e. it can extend without break from a point at or near thefree end of the posterior insertion, through the body portion, andthrough to at or near the free end of the anterior insertion, extendingalong a circumferential path through the implant device).

As described above, the posterior and anterior insertions are preferablyas stiff as possible in axial tension, while also remaining soft enoughfor a surgeon to bend them and thread them through a fixation tunnel orchannel as described below. This allows for strong fixation of theimplant device, and eliminates or reduces micromotion between thefixation and the surrounding bone.

Further advantages of the present invention include provision of animplant device capable of generating variations in surface texture as aresult of its structure as a means to achieve positive interactions withsurrounding tissues.

When implanted at the knee, the implant device of the present inventionis unicompartmental, in that the device is adapted for implantation intoa compartment defined by the space between the tibial plateau and thefemoral condyle. Thus, the device is suited for use in either a lateralcompartment or a medial compartment of the knee. Where it is necessaryto replace menisci in both compartments, two implant devices accordingto the present invention could be used.

While the embodiments described above have addressed the meniscus at theknee by way of example, this technology may also be applied to othersites within the human body, such as the glenoid or acetabular labrum,temporomandibular joint or triangular fibrocartilage of the wrist, withappropriate alterations of the geometry, material properties and tissueattachment means. In particular, the acetabular or glenoid labrum mayrequire multiple attachment/fixations means, around the periphery.

1. An implant system for implantation at a joint, the implant systemincluding an implant device, the implant device comprising: a bodyportion having first and second ends, and a first elongate member,extending from the first or second end of the body portion, the implantsystem further comprising a corresponding fixation device for securingthe first elongate member to a subject, characterised in that thefixation device comprises at least one latching element, the firstelongate member comprising at least one cooperating element, the atleast one cooperating element being capable of cooperating with said atleast one latching element of the fixation device in use.
 2. An implantsystem according to claim 1, wherein the implant device comprises asecond elongate member extending from the other of the first or secondend of the body portion from which the first elongate member extends. 3.An implant system according to claim 2, wherein the implant systemfurther comprises a second corresponding fixation device for securingthe second elongate member to a subject, said fixation device comprisingat least one latching element, the second elongate member comprising atleast one cooperating element, the at least one cooperating element ofthe second elongate member being capable of cooperating with said atleast one latching element of said fixation device in use.
 4. An implantsystem according to claim 1, wherein said at least one latching elementand said at least one corresponding cooperating element comprise aratchet mechanism.
 5. An implant system according to claim 4, whereinthe ratchet mechanism comprises at least one ratchet element and atleast one ratchet stop, the at least one ratchet element being capableof cooperating with the at least one ratchet stop in use.
 6. An implantsystem according to claim 5, wherein the first and/or second elongatemember has a plurality of ratchet teeth.
 7. An implant system accordingto claim 6, wherein: the first and/or second elongate member terminatesin a free end and wherein each ratchet tooth comprises a first surfaceangled relative to said elongate member, the first surface slopingtowards said elongate member in a direction towards the free end of saidelongate member, and a second surface which slopes towards said elongatemember in a direction away from the free end of said elongate member,said second surface being more steeply sloped than said first surface.8. An implant system according to claim 1, wherein at least a portion ofthe first and/or second elongate member is strap shaped or substantiallycrescent shaped in cross-section.
 9. An implant system according toclaim 1, wherein the first and/or second fixation device is adapted tobe secured to a subject's bone in use.
 10. An implant system accordingto claim 1, wherein said fixation device is adapted to be screwed orstapled to bone.
 11. An implant system according to claim 1, wherein thefirst and/or second fixation device is externally threaded, thethreading forming a plurality of latching elements capable ofcooperating with said at least one cooperating element of thecorresponding elongate member, said fixation device preferably being anexternally helically threaded screw.
 12. An implant system according toclaim 1, wherein the first and/or second elongate member is insertablein a tunnel in a subject's bone, the tunnel having first and second openends, the corresponding fixation device being insertable in the secondend of the tunnel, such that the at least one latching element of saidfixation device engages with the at least one cooperating element onsaid elongate member, the corresponding fixation device being securablenon-movably relative to the tunnel, preventing the elongate member frombeing withdrawn from the tunnel via the first open end.
 13. An implantsystem according to claim 1, wherein the implant system furthercomprises an elongate sheath, the first or second elongate member beinginsertable in the sheath, wherein the corresponding fixation device isinsertable in the sheath, and wherein the internal surface of the sheathhas at least one protuberance capable of cooperating with said at leastone latching element on the corresponding fixation device.
 14. Animplant system according to claim 13, wherein at least a portion of thesheath is internally screw threaded, said fixation device beingcorrespondingly externally threaded, such that said fixation device iscapable of securely engaging in the sheath.
 15. An implant systemaccording to claim 13, wherein the sheath has means for non-movablysecuring it to a subject's bone.
 16. An implant system according toclaim 1, wherein the implant device further comprises a reinforcingelement, which extends through the first elongate member and through thebody portion of the implant device, or through the first elongatemember, through the body portion of the implant device, and through thesecond elongate member.
 17. An implant system according to claim 1,wherein said at least one cooperating element of the first and/or secondelongate member comprises at least one aperture for receiving saidcorresponding latching element in use, for directly securing saidelongate member to bone.
 18. An implant system or implant deviceaccording to claim 2 for implantation at a subject's knee joint, one ofthe first and second elongate members being a posterior insertion forsecuring at a posterior region of the subject's tibia and the other ofthe first and second elongate members being an anterior insertion forsecuring at an anterior region of the subject's tibia in use.